As one of vehicle support structures, an aluminum steering knuckle has already been known in JP-A-2014-91468 which has a lower arm connecting portion to which a lower arm is connected.
A steering knuckle transmits a steering or wheel turning force transmitted from a steering arm to a wheel and hence has a complex irregular shape, and therefore, it is general to use a cast product as a steering knuckle. Moreover, a steering knuckle is made of aluminum or a non-ferrous light alloy such as aluminum alloy with a view to reducing the weight thereof so as to realize a reduction in fuel consumption of a vehicle.
Incidentally, to enable a lower arm to be connected to the steering knuckle, an upper surface of the lower arm is counterbored with a T-slot cutter. However, water tends to stay easily in the counterbored portion. On the other hand, with a view to enhancing the connecting rigidity of the lower arm to a lower arm connecting portion of the steering knuckle which is made of the non-ferrous light alloy, in the event that the cylindrical member of the iron based metal is press fitted in the lower arm connecting portion, there are caused fears that an electrochemical corrosion reaction is promoted between the lower arm connecting portion and the cylindrical member by the water staying in the counterbored portion.